COLOMBO, Sri Lanka — Sri Lankan voters decisively rejected former President Mahinda Rajapaksa’s comeback bid, election results showed on Tuesday, leaving this island nation firmly in the hands of officials intent on dismantling most of his policies and completing corruption inquiries that have been closing in on him and his family.

“We have lost a good fight,” Mr. Rajapaksa told Agence France-Presse early Tuesday.

The election, held peacefully on Monday with high voter turnout, determined the makeup of Sri Lanka’s 225-member Parliament. As expected, Mr. Rajapaksa easily won a seat in the chamber. But his political coalition fell short of winning a majority, which he had said would have earned him the right to be named prime minister, the second-most powerful job in the government.

The final results showed that Mr. Rajapaksa’s coalition lost support in every region of the country, including areas long viewed as his political base.

“The election very clearly demonstrated there is no wave of support for him,” said Jayadeva Uyangoda, a professor of political science at the University of Colombo.

Instead, the results strengthened his archrivals: Maithripala Sirisena, the president, and Ranil Wickremesinghe, the prime minister, odd-couple political partners who joined forces to oppose Mr. Rajapaksa.

“We need to unite as one family to create a new political culture in this country,” Mr. Wickremesinghe said in a statement claiming victory on Tuesday. “With one heart, we should strive to ensure our country can meet the challenges of the modern age and rise to the top.”

On Jan. 8, Mr. Wickremesinghe and Mr. Sirisena struck their first blow against Mr. Rajapaksa by defeating his bid for an unprecedented third term as president. In the months since, they teamed up to begin tearing down Mr. Rajapaksa’s most cherished project: building an elaborate ruling structure that gave him and his family immense, unchallenged power over the nation’s military, economy and news media.

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Former President Mahinda Rajapaksa easily won a seat in Parliament, but his political coalition fell short of winning a majority.CreditLakruwan Wanniarachchi/Agence France-Presse — Getty Images

On Monday, by reaffirming the rejection of Mr. Rajapaksa in January, voters guaranteed that the changes begun by Mr. Wickremesinghe and Mr. Sirisena would continue, including nascent efforts to bridge deep divisions left when Mr. Rajapaksa brutally crushed a 26-year Tamil uprising in 2009.

“The majority of this country has voted to consolidate the gains of the Jan. 8 revolution and take forward the policies of good governance and consensus,” Mr. Wickremesinghe said.

The result also increases the likelihood that there will be a careful accounting of Mr. Rajapaksa’s decade in power. His opponents accuse him and his family of plundering billions of dollars from the treasury, a charge he has denied. “Whatever you may say, we are not thieves,” he told reporters last week.

But the roster of his former ministers and close associates under investigation is steadily growing, and several inquiries are now aimed directly at Mr. Rajapaksa and his family.

In April, the Sri Lankan police arrested his brother Basil, the former economic development minister, on charges of misappropriating public funds. The same month, another brother, Gotabhaya, the former defense secretary, was summoned to appear before the nation’s Bribery Commission. In June, his wife, Shiranthi, was questioned by the newly formed Financial Crime Investigation Division.

This month, government sources accused one of Mr. Rajapaksa’s sons, Yoshitha, of ordering the killing of Wasim Thajudeen, a member of Sri Lanka’s national rugby team, in a dispute over a woman. According to officials, three members of his father’s security detail have been identified as the men who abducted, tortured and killed Mr. Thajudeen in 2012.

As part of his campaign this summer, Mr. Rajapaksa had pledged to stop many of those investigations, portraying them as nothing more than a political witch hunt. The loss, though, means “almost certain prosecution” for Mr. Rajapaksa, said Paikiasothy Saravanamuttu, who runs an election monitoring group and a policy research organization in Sri Lanka.

Mr. Rajapaksa had also sought to mobilize voters against a United Nations investigation into allegations of war crimes during the last stages of the war against Tamil separatists. United Nations officials have estimated that as many as 40,000 civilians died in the final assault on the Tamil-dominated north in 2009.

Monday’s results also have significant geopolitical ramifications. As president, Mr. Rajapaksa aggressively courted China, building economic and military ties that alarmed India and the United States. Neither country wants China to gain a larger presence on an island so strategically located along the maritime trade routes between the Bay of Bengal and the Arabian Sea. Mr. Sirisena and Mr. Wickremesinghe have put the courtship on pause, saying the relationship with China needs to be “rebalanced.”

Dharisha Bastians contributed reporting.

A version of this article appears in print on , on Page A6 of the New York edition with the headline: Sri Lankans Reject Ex-President’s Comeback Attempt, and Prosecution May Follow. Order Reprints | Today’s Paper | Subscribe